﻿#define _CRT_SECURE_NO_WARNINGS 1

//编程初学者入门训练第110题
//BC112 小乐乐求和
//https://www.nowcoder.com/practice/ce0b2eacd3d04647831358c2876e44ff?tpId=107&tqId=33393&rp=1&ru=/exam/oj/ta&qru=/exam/oj/ta&sourceUrl=%2Fexam%2Foj%2Fta%3Fpage%3D3%26tpId%3D107%26type%3D107&difficulty=undefined&judgeStatus=undefined&tags=&title=

#include <stdio.h>

int main() {
    long long sum = 0;
    int n = 0;
    scanf("%d", &n);
    for (int i = 1; i < n + 1; i++) {
        sum += i;
    }
    printf("%lld\n", sum);
    return 0;
}